Purpose. Retinal oxygen tension (PO 2 ), photoreceptor oxygen consumption (QO 2 ), the local electroretinogram (LERG), and the vitreally recorded electroretinogram (ERG) were evaluated during retinal artery occlusion in the cat. The feasibility of supplying the retina with oxygen during occlusion by ventilation with 100% O 2 was evaluated. Methods. Double-barreled oxygen microelectrodes were used to measure intraretinal PO 2 and LERGs in anesthetized cats before, during, and after occlusion of

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... single retinal artery. Outer retinal (photoreceptor) QO 2 was determined from retinal PO 2 profiles. Results. During air breathing, occlusion obliterated the LERG b-wave and reduced the vitreal ERG by the amount expected from the area supplied by the occluded vessel. The PO 2 in the entire inner retina was zero, and photoreceptor QO 2 was decreased by approximately 25%. Inspiration of 100% O 2 restored the b-wave amplitude to approximately 50% of normal and increased the amount of O 2 reaching the inner retina. Hyperoxia could not guarantee nonzero PO 2 across the entire retina in either darkness or light, but it elevated the average PO 2 in the innermost 25% of the retina to more than 20 mm Hg. The b-wave amplitude must have been affected by some factor in addition to local hypoxia, because the amplitude was not correlated with inner retinal PO 2 during occlusion, and a normal PO 2 did not result in a normal LERG. Effects of 2 to 2.5 hours of occlusion were reversible if 100% O 2 inspiration was maintained during most of the occlusion. Conclusions. Ventilation with 100% O 2 during occlusion increased the PO 2 across most of the retina and partially restored the LERG b-wave, but the tissue near the vitreous was still sometimes anoxic. The illumination status seemed to make little difference. Inspiration of elevated O 2 might be beneficial in treating retinal vascular occlusive disease, although it alone cannot completely maintain retinal function. Invest Ophthalmol Vis Sci. 1995;36:523-541. XVetinal artery occlusion is a serious disorder that often leads to blindness. As might be expected, it has differential effects on retinal cells.'^ The photoreceptors appear unaffected, whereas the ganglion cells probably stop functioning shortly after occlusion. Changes in retinal cells can be either reversible or permanent, depending primarily on the duration of the occlusion. Irreversible damage to the cells of the inner half of the retina was found histologically in monkeys after retinal artery occlusions of 105 minutes or longer, whereas the outer retina appeared undamaged. 3 Inner retinal function in the monkey, based on From the